[Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m

[David Gilbert]

If your Clipperton amp doesn't have the same problem then it does indeed 
point to the KPA1500.

I don't own a KPA1500, but a quick look at the online manual shows that 
the tuning unit is an L-Network.  Depending upon the load the unit is 
trying to match, an L-Network can require a very large amount of 
capacitance, especially on 160m ... which I suspect is achieved in the 
KPA1500 by switching in high power ceramic units for 160m.  I had to 
replace a couple of high power ceramic doorknob capacitors for 160m in 
my own tube amp because I had degraded them with a high VSWR per my 
earlier post about an overheating common mode choke.

Of course you might not have the same problem, but it would be one of 
the things I'd check.

73,
Dave   AB7E


On 9/2/2020 2:41 PM, Ken Ramirez de Arellano wrote:
> Every bit of antenna hardware ( coax, balun, insulators, etc. have been
> changed out or proven good. Connections are all solid.  My KPA1500 will
> transmit above 800 watts for about 15-30 seconds and then the SWR jumps up
> and it faults out for high VSWR.  I can run 1500 watts on all the other
> “Legacy” bands (10,15,20,40,80) with no problems. I’ve forced an STU
> relearn and still the same issue. The antenna B amp is a Clipperton L and
> that transmits at a KW out and I see no change in VSWR in the external
> wattmeter using all of the same cabling. It’s starting to look like
> something heating up in the KPA1500. Is anyone aware of a known issue for
> this with the KPA1500 or a known fix? I would rather do a field repair
> instead of sending to Elecraft from KP4.  TIA Ken, KP3MM